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CFB > Embryology > Flashcards

Embryology Flashcards

1
Q

What is the blastocyst formed from?

A

Embryoblast = inner cell mass
Trophoblast = outer cell mass

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2
Q

How is the bilaminar disc formed?

A

Outer trophoblast cells are being divided into 2 layers as they are implanted: outer =syncytiotrphoblast, inner = cytotrophoblast
Inner cell mass (embryoblast) is also dividing into 2 layers - hypoblast and epiblast = bilaminar germ disc

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3
Q

What else is formed with the bilaminar disc?

A

Amniotic cavity
Primary yolk sac cavity (below the hypoblast)

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4
Q

What is gastrulation?

A

Formation of the trilaminar disc

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5
Q

What is the primitive streak?

A

An initial thickening and depression in the epiblast

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6
Q

How is the endoderm formed?

A

Cells from the primitive streak migrate inwards and hypoblast cells are replaced by cells from the epiblast, which will form an endoderm.

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7
Q

How is the ectoderm and mesoderm formed?

A

After endoderm, there are a second wave of cells from the primitive streak which go between the epiblast and endoderm to form the mesoderm. The remaining epiblast cells form the ectoderm.

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8
Q

Where is there mesoderm and no mesoderm in the trilaminar disc?

A

Orifices are places where endoderm and ectoderm are in continuity, no mesoderm. Everywhere else there is mesoderm.

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9
Q

What does the intraembryonic mesoderm give rise to?

A

3 parts from medial to lateral area

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10
Q

What is the medial intraembryonic mesoderm and what does it give rise to?

A

Medial part = paraxial mesoderm. Forms somites, giving rise to sclerotome, myotome, dermatome. Vertebral bodies.

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11
Q

What is the middle intraembryonic mesoderm and what does it give rise to?

A

Middle part = intermediate cell mass - gives rise to urogenital system

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12
Q

What is the lateral intraembryonic mesoderm and what does it give rise to?

A

Lateral part = lateral plate mesoderm - gives rise to body cavities, e.g., pericardial, pleural, peritoneal

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13
Q

Summary of what the ectoderm gives rise to

A

Nervous system; sensory epithelia of the eye, ear and nose; epidermis of skin and appendages like hair and nails; maxillary glands; pituitary gland; enamel (ameloblasts)

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14
Q

Summary of what the mesoderm gives rise to

A

Connective tissue (cartilage, bone, blood); striated and smooth muscles; cardiovascular system; genitourinary system; spleen; serous membranes lining the body cavities

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15
Q

Summary of what the endoderm gives rise to

A

Epithelial lining of the GIT, respiratory tract, bladder and urethra; thyroid and parathyroid glands; liver; pancreas

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16
Q

Where do the thyroid and parathyroid glands originate from

A

Endoderm

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17
Q

Where does connective tissue originate from?

A

The mesoderm

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18
Q

Where does enamel originate from?

A

Ectoderm

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19
Q

What happens in neurulation?

A

Notochord influence surface ectoderm to form neural plate, neural groove and thus the neural tube (gives rise to nervous system).

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20
Q

What are cells at the edges of the neural plate and neural tube?

A

Neural crest cells - important in development of the head and neck region

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21
Q

How do neural crest cells become tissues?

A

Neural crest cells transform epithelial cells into migratory mesenchymal cells that contribute to tissue formation. They must migrate to different parts.

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22
Q

What do cranial neural crest cells give rise to?

A

Craniofacial skeleton, cranial ganglia, teeth (odontoblasts), thyroid cells

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23
Q

What forms the pharyngeal arches?

A

Pharyngeal arch mesoderm comes from the neural crest

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24
Q

Where do cranial neural crest cells migrate?

A

Everywhere in the developing head, face and pharyngeal arches region

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25
Q

What is the ossification of the Neurocranium?

A

Upper part - vault = intramembranous
Lower part - base = endochondral

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26
Q

What does the viscerocranium develop from?

A

Some bones are cartilaginous and some are membranous.
The cartilages are from the first and second pharyngeal arches (developing from cranial neural crest cells)

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27
Q

What does neurocranium develop from?

A

Partly from neural crest cells, mainly from paraxial mesoderm

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28
Q

What does the viscerocranium develop from?

A

Neural crest cells

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29
Q

What do laryngeal cartilages develop from?

A

Lateral plate mesoderm

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30
Q

What is intramembranous ossification

A

Flat needle like spiracles develop and radiate from primary ossification centre

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31
Q

What are fontanelle and what are their function?

A

Membranous gaps at future sites of sutures
Allow the growth of skull and brain inside

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32
Q

Main fontanelle

A

Anterior fontanelle at bregma
Posterior fontanelle at lambda
Anterolateral fontanelle at pterion
Posterolateral fontanelle at asterion

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33
Q

Where do the different parts of the Chondrocranium develop from?

A

Anterior to the sella turcica arise from neural crest cells
Posterior to the sella turcica arise from the paraxial mesoderm

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34
Q

Brief description of endochondral ossification

A

Initially small cartilages develop which eventually fuse to form the chondrocranium

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35
Q

What does the first arch divide into?

A

2 processes: maxillary process - maxilla, zygomatic and part of temporal
Mandibular - Meckel’s cartilage, genial tubercles. Rest of mandible develops in the membrane surrounding it (intramembranous ossification)

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36
Q

What part of the viscerocranium does the second arch form?

A

Styloid process by endochondral ossification

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37
Q

What is cranioschisis?

A

Skull fails to form
Neural crest cells are affected causing it

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38
Q

What is craniosynostosis?

A

Early closure of sutures. Causes abnormal skull shape

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39
Q

What is the stomatodeum?

A

Future oral cavity where the ectoderm and endoderm will become continuous with each other

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40
Q

Why are there 5 arches?

A

6 mesodermal thickenings but one disappears

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41
Q

What does the primary yolk sac develop into?

A

The gut tube, forming the foregut, midgut, hindgut

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42
Q

What does the cranial part of the foregut develop into?

A

Oral cavity, salivary glands, pharyngeal apparatus, oesophagus, respiratory system …

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43
Q

How is the buccopharyngeal membrane formed?

A

The membrane lined by the endoderm inside and the ectoderm outside becomes the buccopharyngeal membrane. This will rupture and communicate with the oral cavity. Pharynx larynx respiratory system etc.

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44
Q

How do clefts and pouches form?

A

Ectoderm on the outside. Between 2 arches on ectodermal side is a cleft.
Endoderm on the inside. Between 2 arches on the endodermal side is a pouch.
Core is the mesoderm.

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45
Q

What does the developing neural tube form?

A

Forebrain, midbrain, hindbrain and the spinal cord

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46
Q

How are the upper and lower lips formed?

A

2 mandibular processes fuse in the midline to form the lower lip, followed by the maxillary processes fusing to form the upper lip.

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47
Q

What do the first 3 arched develop from

A

Neural crest cells

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48
Q

What do the first cleft and first pouch develop into?

A

First cleft into external ear
First pouch into middle ear

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49
Q

What are the first and second arch cartilages?

A

First = Meckel’s
Second = Reichart

50
Q

Where do the 4th and 6th arch cartilages develop from?

A

Lateral plate mesoderm since they give rise to the laryngeal cartilages

51
Q

What are the 1st arch cartilage derivatives?

A

Incus, malleus, sphenomandibular ligament

52
Q

What are the 2nd arch cartilage derivatives?

A

(5 s’s) Stapes, styloid process, stylohyoid ligament, smaller Cornu of hyoid, superior body of hyoid

53
Q

What are the 3rd arch cartilage derivatives?

A

Inferior part of hyoid body, greater cornu of hyoid

54
Q

What do the nerves from the arches supply?

A

Sensory branch supplies skin and mucous membranes of the arch
Motor branch supplies the muscles derived from that arch

55
Q

What are the nerves (arising from the hindbrain (medulla and pons)) for each arch?

A

1st - mandibular division of trigeminal CNV3
2nd - facial nerve CNVII
3rd - glossopharyngeal CNIX
4th - superior laryngeal nerve of vagus CNX
6th - recurrent laryngeal nerve of vagus CNX

56
Q

What are the arch arteries for the arches?

A

1st - maxillary
2nd - hyoid and stapedial artery
3rd - common carotid and ICA
4th - left is arch of aorta, right is subclavian artery
6th - pulmonary artery

57
Q

What derives from the 1st cleft?

A

External auditory meatus and canal, outer surface of tympanic membrane.
Auricular hillocks around the first cleft fuse to form the external ear.

58
Q

What happens to the 2nd, 3rd, 4th clefts?

A

They are incorporated into the cervical sinus. This closes the cleft, forming the smooth neck.

59
Q

What can happen if there are anomalies in cervical sinus formation?

A

If part of the cervical sinus remains as a small cystic swelling, you will get branchial cysts along the anterior border of SCM. External communication on skin or pharyngeal wall is a branchial sinus. Internal communication from the cyst towards pharyngeal cavity is a branchial fistula.

60
Q

What derives from the 1st pouch?

A

Tubotympanic reces which gives rise to the auditory tube, tympanic cavity, inner lining of tympanic membrane

61
Q

What does the 2nd pouch give rise to?

A

Palatine tonsil

62
Q

What does the 3rd pouch form?

A

Thymus formed by lower part, inferior parathyroid by the upper part

63
Q

What does the 4th and 5th pouch form?

A

5th pouch is rudimentary. It goes towards the thyroid gland and loses connection with the developing pharynx. It forms the ultimobranchial body, giving rise to the parafollicular (C) cells of the thyroid gland.
4th pouch forms the superior parathyroids.

64
Q

What is Di-George syndrome?

A

Improper neural crest cell migration into 3rd and 4th arch. Causes minor deformities of lower face and thymic and parathyroid aplasia/hypoplasia.

65
Q

What is first arch syndrome?

A

Mandibulofacial dystosis, particular anomalies of the first arch. Mainly deforms the mandible and maxilla.

66
Q

What does internal ear develop from?

A

Otic vesicle

67
Q

What does the middle ear develop from?

A

Tubotympanic reeves gives rise to the auditory tube and middle ear cavity. Ear ossicles are developed from cartilages of 1st and 2nd arches.

68
Q

What is the tympanic membrane derived from?

A

Trilaminar: inner layer from endoderm 1st pouch, middle layer from mesoderm, outer layer from ectoderm of 1st cleft

69
Q

What does the external ear develop from?

A

External auditory meatus and canal - 1st cleft
Auricle (pinna) - fusion of auricular hillocks surrounding 1st cleft

70
Q

What is the pharyngeal floor formed by?

A

Fusion of the ventral part of arches and pouches

71
Q

What does the floor of the developing pharynx give rise to?

A

Thyroid gland, tongue, and respiratory diverticulum

72
Q

What is the opening in the floor of the developing pharynx?

A

Foramen cecum

73
Q

What arises from the foramen cecum?

A

A duct arises from it and descends down. In the neck region it will divide into 2 lobes, developing into the thyroid gland. Duct = thyroglossal duct

74
Q

Where is the foramen cecum seen?

A

At the junction of the anterior 2/3 of the tongue and posterior 1/3 of tongue

75
Q

What happens to the thyroglossal duct?

A

The top of it will obliterate and it will lose connection with the tongue. Only the pyramidal lobe remains here.

76
Q

Is the thyroid gland ectodermal, mesodermal or endodermal?

A

Endodermal

77
Q

How is the thyroid gland developed?

A

Starts at the thyroid diverticulum from floor of pharynx between 1st and 2nd arches. Thyroglossal duct forms. Thyroid descends in the neck in front of the hyoid and larynx and becomes bi-lobed. Upper thyroglossal duct disintegrates. Thyroid gland reaches final position. Endodermal cells of thyroglossal duct form thyroid follicles. Ultimobranchial body forms C cells. Connective tissue and capsule are derived from surrounding mesoderm.

78
Q

What is the levator glandulae thyroidae?

A

Upper non-glandulae fibrous extension, extending to the hyoid bone

79
Q

Congenital anomalies of thyroid gland

A

Total agenesis
Ectopic thyroid - develops in wrong place
Thyroglossal cyst if duct stays without disintegrating

80
Q

Anatomy on the ventral surface of the tongue

A

Lingual frenulum

81
Q

Anatomy on dorsal surface of the tongue

A

V-shaped sulcus terminalis to separate the anterior and posterior
Circumvallate papillae in front of sulcus terminalis
Lingual and palatine tonsils in the posterior 1/3
Palatoglossus and palatopharyngeus and their arches
Epiglottis with median glossoepiglottic fold, lateral epiglottis fold and epiglottis vallecula

82
Q

How does the tongue develop (big explanation)

A

In the first arch in floor of pharynx, there are 2 lingual swellings on either side of a swelling called the tuberculum impar. Foramen cecum between 1st and 2nd arch. Thickening of the third and fourth arch = hypobranchial eminence.
Lingual swellings and tuberculum impar fuse, forming anterior 2/3. Cranial part of hypobranchial eminence grows and fuses with these in a v shape creating sulcus terminalis. At the junction of this v is the foramen cecum. The caudal part of hypobranchial eminence will develop into the epiglottis. Median and lateral glossoepiglottic fold develop from the 4th arch. The posterior 1/3 overgrown and develops into Circumvallate papillae.

83
Q

What does the epithelium and anterior 2/3 develop from?

A

1st arch

84
Q

Where are the posterior 1/3 and Circumvallate papillae of tongue derived from?

A

3rd arch

85
Q

What does thickening of the third and fourth arch create in relation to the tongue?

A

Hypobranchial eminence

86
Q

What forms the anterior 2/3 of the tongue?

A

Fusion of the lingual swellings with each other at the midline and tuberculum impar

87
Q

How is the sulcus terminalis formed?

A

Cranial part of hypobranchial eminence grows and fuses with these in a v-shaped area

88
Q

What does the caudal part of the hypobranchial eminence develop into?

A

Epiglottis

89
Q

Where do the median and lateral epiglottic folds develop from?

A

4th arch

90
Q

What origin is the mucosa of the tongue from?

A

Endoderm

91
Q

What mytotomes form the tongue?

A

Occipital myotomes migrate in the developing tongue and form muscles of the tongue. They drag along the hypoglossal nerve with them, which supplies all muscles of the tongue except the palatoglossus supplied by the vagus nerve because it is derived from the 6th arch.

92
Q

Sensory nerve supply and arch derivations from every part of the tongue

A

Anterior 2/3 (1st arch) - GS lingual nerve; SS chorda tympani
Posterior 1/3 and Circumvallate papillae (3rd) - GS and SS glossopharyngeal nerve CNIX
Posterior most part (4th arch) - GS and SS - vagus nerve (superior laryngeal)

93
Q

How does the tongue separate from the floor of the pharynx?

A

The deepening of the linguogingival sulcus separates it so it is only attached to the floor at the root, so it can protrude.

94
Q

Anomalies of the tongue

A

Apoglossia - absence of the tongue; microglossia, macroglossia, Bifid tongue (failure of fusion of lingual swellings), ankyloglossia - short frenulum due to defective separation

95
Q

What separates the floor of the stomodeum from the foregut?

A

Buccopharyngeal membrane

96
Q

What happens when the buccopharyngeal membrane ruptures?

A

External stomodeum becomes continuous with the oral cavity.

97
Q

Where is the buccopharyngeal membrane in adults?

A

Between the vestibule (ectodermal) and oral cavity proper (endodermal)

98
Q

The mesoderm covering the developing forebrain proliferates to form a downward projection called what?

A

Frontonasal prominence

99
Q

How does the face develop?

A

Ectoderm overlying the frontonasal prominence shows bilateral thickenings - nasal placoderms. Nasal placoderms sink below the surface forming nasal pits with 2 raised margins, medial and lateral nasal prominences. Stomodeum is in continuity with the nasal pits. 1st arch gives rise to the maxillary and mandibular prominences which form the upper and lower lips. Maxillary prominence grows medially and fuses with lateral and medial nasal prominences.

100
Q

How does the nares form?

A

Nasal pits are separated by stomatodeum, forming the anterior nares. Frontonasal prominence narrows so the nares come closer.

101
Q

How does the nasolacrimal duct form?

A

Nasolacrimal groove at junction of maxillary and lateral nasal prominences. Lacrimal sac and nasolacrimal duct form from ectodermal cord.

102
Q

Where does the nasolacrimal duct run?

A

From the medial angle of the eye to inferior meatus of nasal cavity

103
Q

Brief formation of the external nose

A

Frontonasal prominence narrows to become bridge
Maxillary process fuses with lateral and medial nasal processes to separate nares from stomatodeum
Medial fuse to form crest and tip of nose, lateral forms the sides
Phil trim (between nose and upper lip) develops from the medial nasal prominence, with skin over it from maxillary process

104
Q

Summary: what does the frontonasal prominence derive?

A

Forehead, bridge of nose, and medial and lateral nasal prominences

105
Q

Summary: what does the maxillary prominence derive?

A

Cheeks, lateral portion of upper lip, upper jaw (hence maxillary nerve supply)

106
Q

Summary: what does the medial nasal prominence derive?

A

Philtrum of upper lip, crest and tip of nose, inter maxillary segment

107
Q

Summary: what does the lateral nasal prominence derive?

A

Alae or nose

108
Q

Summary: what does the mandibular prominence derive?

A

Lower lip and lower jaw (hence mandibular nerve supply)

109
Q

Overview of palate formation

A

Part of medial nasal process will grow in between 2 maxillary processes, inside, giving rise to the primary palate. Additional processes coming from maxillary process will develop into secondary palate. Primary and second palate fuse to form definitive palate. Palatial shelves are elevated and fused. Ossification of anterior 2/3 forming hard palate and posterior 1/3 remains unossified forming the soft palate.

110
Q

What does the primary palate develop from?

A

Intermaxillary segment (philtrum of upper lip, median portion with central 4 upper incisors, triangular portion of palate).

111
Q

How does the secondary definite palate form?

A

Secondary palatial shelves/lateral palatal processes coming from maxillary process, fuse with the primary palate, nasal septum and each other. At the junction is the incisive foramen.

112
Q

Why do palatial shelves elevate?

A

Developing tongue pushes them vertical but they need to be elevated to become horizontal to fuse.

113
Q

How does palate fuse?

A

Horizontal palatial shelves fuse. Anterior part ossifies while posterior part remains unossified with muscles developing into it, and creating an extension called the uvula.

114
Q

Where are anterior and posterior clefts usually seen?

A

Anterior clefts usually in primary palate, in front of incisal foramen
Posterior clefts usually in secondary palate, posterior to incisal foramen

115
Q

Why do anterior and posterior clefts appear?

A

Anterior clefts - failure of fusion of maxillary and medial nasal processes
Posterior clefts - failure of fusion of palatial shelves

116
Q

Dental and skeletal problems associated with CL and or CP

A

Hypodontia, tooth agenesis, supernumerary teeth enamel hypoplasia, ectopic eruptions, malocclusions

117
Q

Spina’s classification of clefts

A

Group I: preincisive foramen clefts - anterior to incisal foramen
Group II: transinsicive foramen clefts - anterior and posterior. Start from anterior cleft and crosses foramen to go posteriorly.
Group III: post-incisive foramen clefts - posterior clefts. Can result in bifid uvula, cleft in soft palate with fuse hard palate, or unfused both palates
Group IV: rare facial clefts

118
Q

What other problems are associated with CL and CP?

A

Nasal, feeding, ear, speech

119
Q

What is treacher-Collins syndrome?

A

Small mandible and facial bones with ear malformation
Type of first arch syndrome

120
Q

What is Pierre robin syndrome?

A

Micrognathia (small mandible) with cleft palate as well as defects of eyes/ear
Type of first arch syndrome

121
Q

Where are the salivary glands derived from? Ectoderm or endoderm?

A

Parotid from epithelium lining the vestibule so endoderm
submandibular and sublingual from epithelium lining the oral cavity proper so endoderm

122
Q

Developmental anomalies of salivary glands

A

Aberrant or ectopic; aplasia or hypoplasia; hyperplasia; accessory duct

CFB (34 decks)

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